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Discussion Starter #1
Hey so I'm planning on doing a build, partly as a school project, partly because I've wanted to for a while now.

So I am planning on taking an older model bike such as a Honda CB750 and swap the motor for something like a CBR600RR or R6 engine and put newer suspension on it. I may have a line on a R6 (I believe it's a 2000) through my internship @ Capitol Yamaha as a donor bike for the engine and suspension.

Any tips or advice would be greatly appreciated. Thank you.
 

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the frame can't nearly handle the power that engine is putting down
 

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Discussion Starter #3
do you have any advice on how i can make it work? This is something that I have been wanting to do for quite some time now. In my mind its the next evolution of cafe racers, because they started by doing engine swaps and dropping weight. Thank you.
 

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There is a huge difference between a slow heavy CB750 motor and say an R6. To put that in perspective, the fastest CB750 motor would struggle to make 100HP and any R6 makes that out of the box with horses to spare. They are generations apart.

For sure we used to swap one heavy underpowered motor for another heavy and slightly less underpowered motor, but we are talking generational differences here. Compare a light rigid R6 frame and swingarm with an old flexy CB750 and there just is no comparison in terms of stiffness and geometry is very different as a result of that.

You could take a crashed R6 and strap its powerplant in a jig with stock R6 suspension and brakes and build a trellis frame around those parts using a CB750 steering head and pretend that the frame is more or less stock CB750 but there's not a lot of point.

So teh question here is what is the next fashion trend? It might be naked fighters in more of a cafe race look or maybe Street fighters or an updated AMA superbike look, but I don't think so. Cafe racers embody the spirit of the sixties and seventies - not very fast but they feel fast and are basic motorcycles. AMA superbikes were the next generation of racers and bikes like the ELR copied that look a little way down the track.

I'd suggest maybe a modern single cylinder motor and suspension in an old school frame. Is there such a thing as a modern single? Well maybe not so many, so that leaves twins - perhaps a HD in a Cafe race looking chassis or maybe the Virago will be redeemed and will rise as the next gen cafe racer.

Probably naked Kawasaki or Honda 300's are the next big thing - looking like Moto3 race track refugees with echos of teh past in the styling.

Maybe it's early FZR and CBRs made to look like Moto2 or MotoGP bikes.
 

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I understand the appeal of using a more modern motor, suspension, brakes and electrics in an older chassis because you could increase the reliability and more riding versus less wrenching time. The problem is, as has been pointed out, the frame can't handle the HP and the suspension loads. So, the trick is to brace the frame so it will handle more suspension loads, stay away from big tires, huge brakes and USD forks. Finally stay away from high HP new motors. For an upgraded CB750, I would look at the first generation CBR600F motor, front suspension, brakes and wheels. Brace the CB750 swing arm or find a period replacement. Keep the twin shocks and transfer the entire electrical system. The CBR had about 80 RWHP, 37mm forks, a 110 -17 front tire and a 140 or 150 -17 rear. With the 750 frame and bodywork it would still be heavy and not great handling but it would be good. You can find a complete CBR600F for under $1000.

If you work at a Yamaha dealer then an FZR600 would work just as well, although it has a few more HP. A Seca II aircooled would work and has about 60HP (claimed 70 at the crank)


Ken
 

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Discussion Starter #6 (Edited)
Alright. Thanks everyone, maybe I'll just build up a racer without swapping the engine. You certainly gave me a lot to think about, and you know more than I do so your advice means a lot.

That being said, if you have an idea on how I can do the swap, let me know as i have been thinking of this for over a year now. Just keep in mind that my resources and budget are fairly limited as I', only 17.

Would it be any easier/more feasable with a KZ1000?

Thanks again,
Seth
 

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get a cbr600, or an fzr600, or something like that, and make it look like an old shitbox. actually, the honda hornet had a spine frame with everything else modern. get a 900 hornet and fit an old tank to it.
 

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You are thinking about this like people think about cars and engine swaps. You can't do that with a motorcycle because as has been mentioned the engine and frame are structurally tied together.

As as you are 17, I am going to assume you do not have a motorcycle license or riding expirence. Instead of a project, how about you go and get those instead. But a bike, a running riding one, and get a license, and then use the bike to get around for two years wile fixing and maintaining the bike yourself.
 

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KZ1000s are some of the most ill handling bikes, unless you do a lot of CAREFUL work bracing them.

It's just as pointless to put a modern engine in one of those than it is to do it to a CB frame.

You'd be amazed at what you can do with a 70s Triumph with some modest suspension upgrades and good tires. They are more than an average rider can handle on a track. I have a hard enough time with my late 60s 650 Triumph, we're about equally matched. On a modern bike, I'm no slouch. Ever ridden a Kawasaki ZRX? I've had 3 of them; a 1200 in my garage right now. It's what the KZ would have naturally progressed to, but they made a quantum leap and covered everything in perimeter frames and plastic instead. It was smart of Kawasaki to take a step back the way they did.
 

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if you're on a limited budget, go try to set up your cb750 with good suspension and tires, I bet you'll shoot your budget to shit before you can even touch a cutoff wheel. I think some of the psychology of projects like that is that you have a subconscious fear of failure, so you propose a project so ungodly complex and expensive, that you'll never have to come close to completion and potential failure, "it always works great before you ride it!". so start smaller, fail a lot, learn a lot, really crazy projects are successfully completed as an evolution rather than a ground up "never seen asphalt until it was all the way done" deal
 

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All the power in the world is useless, if you can't put it to the ground.

And Not wanting to knock anybody, or to insinuate that I have any idea how well Anybody here rides;
But you can tell the riders who have ridden a bike to the point of knowing what frame flex feels like.
 

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Let's just put aside the points that have already been mad about the weakness of the CB frame (or any old cradle type frame, for that matter). Lets just look at the space restrictions you are looking at. Here is a 3D rendering of an R6 motor:



Here is a CB750 motor:


Do you notice two blaring problems (or differences).

1. That huge thing on the front of the R6 motor, that isn't on a CB. That's right, the radiator!
2. The carbs on the R6 point UP....as into the space where the fuel tank goes. Or more specifically where the back bone of the frame would be. (There are very important reasons why they put them there, that I am not going to take the time to go into, right now.)

Compare the frame differences....
R6:


CB750:


Notice the lack of tubes or bracing that the R6 frame has above the motor. Also notice how much larger the frame is on the side of the frame as it runs beside the motor, not above it. You also need to know that that big beefy frame isn't enough. The R6 motor is a stressed member of the frame. That means it becomes PART of the frame when it is bolted up. The amount of hacking and modification you would need to do to an old school frame just to fit a modern engine would be enormous, and you would most likely end up with a bike that was completely dangerous.

Now educate us old farts how "started by doing engine swaps and dropping weight". As Teaser mentioned, any engine swaps that were done back in the day, were basically the same configuration, or type of engine.
 

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so here's a thought...

take the motor and put it in a go-cart frame. those are simple enough to make yourself if you are a decent welder, and it would be a blast to drive around in.
 
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So, now that you have had a variety of inputs here, if you already have the CB750, then do as has been suggested and just ride it while making upgrades to the suspension and ergonomics. That will keep you broke and busy for years to come. If you don't already have the CB750, don't get one. Since you are affiliated with a Yamaha dealer, look at some of these models; Seca 550, FJ600, FZ600, Radian YX600, or Seca II 600. These are all aircooled. 2 valve DOHC motors that are from 1981 - 1993. They will be reliable and easy to work on. They have spine type frames except the FZ and the Seca II which have steel perimeter frames that were transitional to the Delta box frame of the FZR series and continues in sportbikes today. Yamaha is very good at parts bin engineering so many parts such as front forks and swingarms are easily interchangeable between models. The same goes for wheels and brakes.

Ken
 

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Discussion Starter #16 (Edited)
"As as you are 17, I am going to assume you do not have a motorcycle license or riding expirence. Instead of a project, how about you go and get those instead."

Actually sir I have both my licence and riding experience. And i have been working on/maintaining my current 89 Katana 750 which I had to ressurest to ride in the first place, so if you aren't going to offer any real advice then just don't add onto here
 

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So what is the actual point of this stupid idea?
I don't understand "work for the sake of work"
At the end you will have a whole that is less then the sum of its parts.

Why don't you figure out how to keep a vintage bike running for a while, then figure out some functional improvements to it.

Clearly you didn't bother to read anything on this forum before starting this tread. If you had then you might have had a chance of seeing how dumb the idea would sound to us here.
If you want actual advice and help then get you junk together. If all you are looking to do is waste time, play dress up and all that jazz then speak up. A recommendation for someplace else to go can be made.
 

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My point of mentioning a 70s Triumph is that they are far easier to find in decent, running shape, with title, than a CB750 is ever likely to be.

Plus, the performance is not far off the CB750, at 100 lbs less weight.
 

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Let's just put aside the points that have already been mad about the weakness of the CB frame (or any old cradle type frame, for that matter). Lets just look at the space restrictions you are looking at. Here is a 3D rendering of an R6 motor:



Here is a CB750 motor:


Do you notice two blaring problems (or differences).

1. That huge thing on the front of the R6 motor, that isn't on a CB. That's right, the radiator!
2. The carbs on the R6 point UP....as into the space where the fuel tank goes. Or more specifically where the back bone of the frame would be. (There are very important reasons why they put them there, that I am not going to take the time to go into, right now.)

Compare the frame differences....
R6:


CB750:


Notice the lack of tubes or bracing that the R6 frame has above the motor. Also notice how much larger the frame is on the side of the frame as it runs beside the motor, not above it. You also need to know that that big beefy frame isn't enough. The R6 motor is a stressed member of the frame. That means it becomes PART of the frame when it is bolted up. The amount of hacking and modification you would need to do to an old school frame just to fit a modern engine would be enormous, and you would most likely end up with a bike that was completely dangerous.

Now educate us old farts how "started by doing engine swaps and dropping weight". As Teaser mentioned, any engine swaps that were done back in the day, were basically the same configuration, or type of engine.


Its not impossible Sethh it has been done go for it . JUST DO IT show these negative Nelly's :cool:
 

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"As as you are 17, I am going to assume you do not have a motorcycle license or riding expirence. Instead of a project, how about you go and get those instead."

Actually sir I have both my licence and riding experience. And i have been working on/maintaining my current 89 Katana 750 which I had to ressurest to ride in the first place, so if you aren't going to offer any real advice then just don't add onto here
Probably should have opened with that so we would know that you are only very inexpirenced instead of extremely inexpirenced. Seriously, keep to riding your oil boiler katana and forget this foolishness.

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Its not impossible Sethh it has been done go for it . JUST DO IT show these negative Nelly's :cool:
wow, what a complete joke of a motorcycle.
 
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